1. Field of the Invention
This invention relates to a digital audio signal recording unit for recording digital audio signals on a sound track on a motion picture film for forming a digital sound track, and an audio signal recording system in which the digital audio recording unit is combined with an analog audio signal recording unit for recording analog audio signals on the motion picture film for forming an analog sound track in such a manner that the digital sound track having the digital audio signals recorded thereon and the analog sound track having the analog audio signals recorded thereon may be simultaneously formed on one and the same motion picture film. More particularly, it relates to a digital audio signal recording unit combined with an analog audio signal recording unit in such a manner that both the analog audio signals and the digital audio signals may be recorded during travel of the motion picture film from a film supply side to a film take-up side.
2. Description of the Related Art
The motion picture film is constituted by an area in which the pictures have been recorded and an area in which the audio signals have been recorded. The pictures are discretely recorded in a series of frames provided at the center along the length of the motion picture film. The audio signals are usually recorded on the motion picture film in the form of analog signals. The audio signals, recorded in the state of analog signals on the motion picture film, are recorded in an analog sound track area provided between the frames dedicated to the pictures and a series of perforations formed on both longitudinal edges of the motion picture frame and adapted for being engaged by a feed mechanism used for feeding the motion picture film.
There is also proposed a motion picture film in which analog audio signals are recorded after modulation into digital audio signals. The digital audio signals may be recorded on the motion picture film without being adulterated with noise components and are not susceptible to deterioration in the playback audio signals even on repeated reproduction of the motion picture film. Sound reproduction of extremely high quality may be achieved by employing digital audio signals as the audio signals recorded on the motion picture film.
If the digital audio signals are recorded on the motion picture film in substitution for analog audio signals, the digital signals are recorded in the analog sound track area in which the analog audio signals are conventionally recorded.
Some of the projectors used for replaying the motion picture film are capable of replaying only the motion picture film carrying the analog audio signals, while being incapable of replaying the motion picture film carrying digital audio signals. Consequently, the motion picture film carrying digital audio signals also has analog audio signals recorded thereon so that it may be reproduced by a projector designed to replay only the motion picture film carrying the analog audio signals. When recording the digital audio signals along with the analog audio signals, the digital audio signals are recorded in areas outside of the rows of perforations formed along both longitudinal edges of the film, areas between the perforations or in areas between frames dedicated to picture recording.
For recording the audio signals on the motion picture films, an audio signal recording unit dedicated to a motion picture film adapted to record only the audio signals is employed. There has been proposed an audio signal recording unit of this type which is capable of recording both the analog audio signals and the digital audio signals. When recording both the analog and digital audio signals by such recording unit, the analog audio signals are first recorded as the film is run in one direction. The film, now having the analog audio signals recorded thereon, is then rewound and again run in the one direction and the digital audio signals are recorded on the running film. Consequently, should the analog and digital audio signals be recorded using the audio signal recording unit, an operation of rewinding the elongated motion picture film is necessitated, thus complicating the process of forming the analog and digital sound tracks. In addition, the mechanism of running the motion picture film is also complicated, while the overall recording unit becomes bulky in size.
Furthermore, the audio signal recording unit capable of recording both the analog audio signals and digital audio signals has to be employed in place of an audio signal recording unit capable of recording only the analog audio signals. Thus there is no necessity of providing the audio signal recording unit for the motion picture film capable of recording only the analog audio signals.